ABSTRACT
Background: COVID-19 in Africa was less severe with fewer reported cases, hospitalizations and deaths compared to other continents. However, the lack of adequate surveillance systems in Africa makes estimating the burden of infection challenging. Serosurveillance can aid in determining the frequency of infection within this population. This study is aimed to estimate SARS-CoV-2 seroprevalence, describe the SARS-CoV-2 antibody (Ab) levels, and examine associations of seroreactivity among Ugandan blood donors. Method(s): Samples were obtained from the Mirasol Evaluation of Reduction in Infections Trial (MERIT), a randomized, double blind, controlled clinical trial evaluating transfusion transmitted infections. MERIT blood donor samples (n=3,517) were collected from Kampala, Uganda between October 2019 to April 2022. Additional blood donor samples (n=1,876) were collected from around the country between November-December 2021. Samples were tested for Ab to SARS-CoV-2 nucleocapsid (N) and spike (S) using an electrochemiluminescence immunoassay assay (Meso Scale Diagnostics, Gaithersburg, MD) per manufacturer's protocol. Samples seroreactive to both N and S Ab were considered Ab positive to SARS-CoV-2. Seroprevalence among MERIT donors were estimated within each quarter. Factors associated with seroreactivity from November-December 2021 were assessed by chi-square test. Result(s): SARS-CoV-2 seroprevalence increased from < 2.0% in October 2019- June 2020 to 82.5% in January-April 2022. Three distinct peaks in seroreactivity were seen in October-November 2020, July-August 2021, and January-April 2022 (see Figure). Among seroreactive donors, median N Ab levels increased 9-fold and median S Ab 19-fold over the study period. In November-December 2021, SARS-CoV-2 seroprevalence was higher among donors from Kampala (58.8%) compared to more rural regions of Hoima (47.7%), Jinja (47.9%), and Masaka (54.4%;p=0.007);S seroprevalence was lower among HIV+ donors (58.8% vs. 84.9%;p=0.009). Conclusion(s): Blood donors in Uganda showed high prevalence of Ab to SARSCoV- 2 by March of 2022, indicating that the infection levels were similar to many other regions of the globe. Higher seroprevalence was observed in the capital compared to more rural areas in Uganda. Further, increasingly high antibody levels among seropositive donors may indicate repeat infections. The lower COVID-19 morbidity and mortality was not due to a lack of exposure of the virus, but other factors yet to be determined.